1. Field of the Invention
The present invention relates to a semiconductor memory device and a driving method thereof.
2. Related Art
In recent years, nonvolatile memories such as NAND flash memory have been further miniaturized. When an interval between adjacent memory cells becomes small, along with the miniaturization of devices, proximity effect between the memory cells becomes distinctive. The proximity effect is interference that memory cells receive from adjacent memory cells due to capacitance coupling between adjacent plural memory cells and the like. For example, data stored in the memory cells receives influence of charge accumulated in memory cells adjacent to the memory cells storing the data. When the interval between the adjacent memory cells becomes smaller, the influence of the charge in the adjacent memory cells becomes large.
When the influence of the proximity effect becomes distinctive, a noise component contained in a cell current at the data reading time and back pattern noise which looks like a change of the cell current depending on data written in the cells become large. Further, when a processing size of a memory cell array is miniaturized, the nose component becomes relatively large when the cell current is small. When noise in the cell current is large, time required for a sense amplifier to sense data increases. Further, when noise in the cell current is large, there is a risk that the sense amplifier erroneously detects data.